A study of the influence of LiI on the chain conformations of poly(ethylene oxide) in the melt by small-angle neutron scattering and molecular dynamics simulations

Small-angle neutron scattering (SANS) experiments and molecular dynamics (MD) simulations have been performed on poly(ethylene oxide)/LiI solutions at a salt concentration corresponding to ether oxygen:li = 1.5:1. Both SANS measurements and simulations revealed a substantial reduction (10-15%) in the radius of gyration of PEO chains in the PEO/LiI solutions compared to chains in the pure melt. The characteristic ratio of PEC chains in the melt as obtained from simulations compared well with the values from SANS experiments. Detailed analysis of the MD trajectories revealed a broad distribution in the number of ether oxygen atoms per 12 repeat unit chain involved in Li+ cation complexation, with a strong preference for zero, three, and six ether oxygen atoms per chain. Chains not directly involved in cation complexation (zero complexing ether oxygen atoms) were found to have chain dimensions similar to those in the pure melt. Chains with one to three ether oxygen atoms involved in cation complexation actually showed an increase in radius of gyration. Chains with four or more ether oxygen atoms involved in cation complexation showed increasingly narrow radius of gyration distributions and decreasing radius of gyration, reflecting tight wrapping of the chains around the Li+ cations.